From my experience, doing ferulic rests produce only subtle changes in flavor. So subtle that I'm not even sure it's due to the ferulic rest itself, so I skip it on my wheat beers now. The most significant impacts on the flavor of a German wheat beer for me have been the yeast pitch rate, pitch temperature, and fermentation temperature.
I get banana flavors no matter what I've tried. The challenge for me has been to tone the esters down enough so that the clove-like phenols come through as well. My favorite hefes are made using WLP380, slightly over pitched, pitched at 60F and allowed to ferment no warmer than 62F for most of the fermentation. Close to the end of fermentation I will let it free rise a few degrees to finish. I get equally good results doing the same with WLP300 and Wyeast3068. I just prefer the flavor of WLP380.
On the Jamil Show, they talk about how you really do have to ferment these cold to get a good flavor from a German wheat beer yeast. 60-62F is what works for me. Any higher than that and I get a grossly unbalanced beer with tons of esters. Too much banana, no clove. I also make a slightly larger starter than what Mr.Malty tells me I should use, usually about 1/2 liter more.
In German wheat beers, I aim for an OG of 1.048-1.050 and an IBU of 12-14. Too much hops and malt, and the yeast character gets masked, in my opinion.